The present invention is directed generally to an actuating device for a brake unit of an electronically controlled vehicle brake system.
A typical electronically controlled vehicle brake system (EBS) is equipped with a purely pneumatic single circuit and with an electropneumatic circuit. The electropneumatic circuit includes, among other elements, an electronic control unit (ECU) and a brake signal transmitter with an integrated set value sensor designed as a displacement sensor, brake switch and proportional relay valve. The brake signal transmitter is connected mechanically to the vehicle brake pedal and electrically to the ECU. The brake signal transmitter (i.e., the brake unit) is provided with a tappet mechanically connected to the brake pedal and disposed in axially displaceable relationship inside the housing of the EBS brake unit. The tappet actuates a piston via a component that introduces some lost motion (i.e., idling stroke) and a spring braced against the piston and against the component. The piston operates a brake valve. The idling stroke (about 2 mm) is provided to ensure that the vehicle driver has some margin during brake actuation and does not instantly actuate the vehicle brakes. The tappet movement is communicated to the ECU by the displacement sensor, which is provided with one part in fixed position in the housing and with a slide that can move in axial direction together with the tappet, the slide engaging receiving means of the tappet.
Difficulties can arise in guiding the tappet and the component that introduces the idling stroke in such a way that minimizes friction. When the brake pedal is actuated, the tappet is exposed to not only an axial force, but also a torque which causes the tappet to twist around its longitudinal axis, especially when the mechanical connection to the brake pedal is a ball-and-socket joint. Under these conditions, the slide of the displacement sensor might slip out of its receiving means in the tappet or become damaged, thus making displacement sensing impossible or ineffective.
Accordingly, it is desired to provide an actuating device of the type under discussion in which the moving parts are guided with sufficiently low friction and any torque acting on the tappet is compensated for.